VoxSolaris: The Voice of the Sun
Making trains work
 

Do trains have a future?

Trains are an enduring concept but not a particularly practical or economic one. On a cost per journey basis, trains rarely beat cars even in spite of being subsidized while the latter is heavily taxed. And although trains can travel faster than cars in most cases, overall door to door journey times are in many cases longer. And trains go when they want to and not when you want to. Trains beat cars only when the car is placed at a disadvantage such as to outweigh all of the above. When traveling into London for example, cars are beset with appalling traffic conditions, punative congestion tolls and outrageous parking charges. And if you don't have a car or even a driving license then you have no choice. And if you are an awfully important person who absolutely must be online and on the phone at all times you also have no choice. In short, trains win only when they can do something the car cannot do.

The advent of the self driving car might still be a few years off but when it does come trains have got a problem, particularly in the UK where trains are very expensive, comparatively slow, unreliable and due to chronic overcrowding, uncomfortable if you can't get a seat. The self driving car is an equalizer. You won't need a drivers license to use one. You won't be hit by parking charges either because worse case, you can just send it home. In any event, you won't need to own the car. They can be publicly owned and hailed like cab. And you can do what you like in them. Send emails, argue with people on the phone, play video games or put you feet up and sleep. And the cost per journey? That will have to be comparable to the cars of today. If it cost as much to drive as it does to ride the train the economy would be in terrible shape. One could ask, do trains have a future?

The New Golden Age: Can trains beat planes?

The one advantage trains will always have over cars, at least on long journeys, is speed. In the UK trains can hit 125 mph. In Europe it is 180. In Japan and more recently China, mag-lev trains can do something like 300 mph. How far could train technology go? Could trains beat planes?

If we put a mag-lev train inside an evacuated tube we remove the main limit on the speed. The air resistance at 300 mph is astronomical as the force rises as the square of the speed. Moreover, at those speeds the train will experience significant lift, making the job of stabilizing the train more difficult and a derailment more likely. Take away the air and we not only remove this problem, we also massively reduce energy consumption. The train becomes by far, the mode of travel that consumes the least energy per passenger mile and the speed is only limited by two things. Firstly the length of the journey must be such that we can actually reach a target speed before we have to break in order not to overshoot, and secondly, the quality of the track. The faster you go, the finer the tolerance has to be. If we were prepared to spend the money on very highly engineered tracks, the next limit would be orbital speeds.

Exiting though this is, there is no point going down this path when existing mag-lev track is still far too expensive to build an extensive network. But there is a way to make mag lev a lot cheaper. It's called partial mag lev. This is a hybrid between a traditional railway track and a mag-lev. Instead of energizing the mag-lev coils to support 100 percent of the train's weight, it is set to support 99 percent with a tolerance of 0.5 percent either side. The remaining 0.5 to 1.5 percent of the train's weight is supported by rail using wheels constructed using composites. If we used steel for the wheels the speeds would be limited to about 300 mph because the centrifugal forces in the wheel above that speed would tear it apart. Composite materials have some 16 times the specific strength of steel and can rotate 4 times as fast giving a theorectical top speed of 1,200 mph.

The wheels would give rise to frictional losses but with an average of 99 percent of the train's weight being handled by the mag-lev, these loses would average just 1 percent of the normal value. By forgoing a mere 1 percent of the potential frictional savings offered by mag-lev we have eliminated two of the major costs of mag-lev. Firstly the miriad of sensors needed to detect how near the train is to the track and the expensive computer controlled and ultra fault tolerant curcuitry needed to adjust the strength of the magnetic field, can be dispensed with. This function is now performed by weight sensors between the wheels and the train. As the weight rises and falls with passenger load, the field is adjusted. Any overshoot or undershoot will not result in a derailment as the depth of the wheels seated on the track is too great for the train to break loose. Secondly, the mag-lev part of the track can now be engineered to a courser tolerance as it no longer needs to be quite so smooth.

Now the only problem we were left with was the tolerance of the track alignment itself. If we use the traditional twin track we could align the tracks accurately enough for speeds of up to 1200 mph as long as we were going in a perfect straight line. But as soon as we turned the slightest corner then it becomes a rather different matter. But replace this with a single rail with a deep grove in which the wheels sit and this problem goes away. This eliminates the need for switchable points as the train can now switch to the left or the right by steering (albeit at slower speeds). Where the two rails would normally be on either side, there are two flat rails upon which spring loaded stabilizer wheels run. These do not have to be as accurately aligned as the twin track would be and as a consequence it is much cheaper to build per mile. One could be more daring and replace the stabilizer mechanism by means of gyroscopes placed on top of the train.

£50 billion on HS2? If by the time it is built it is not a white elephant it will still be a wasted opportunity. And it is not as though this is even a new idea. Elon Musk recently proposed something similar but there are records of this concept being discussed back in 1909. And let us not forget another advantage of the evacuated tube. There can be no possibility whatsoever of the wrong type of snow or the wrong type of leaves on the track.